Two-layer expansible linkage of high flexibility



1960 D. JACOBSEN 2,949,729

TWO-LAYER EXPANSIBLEI LINKAGE OF HIGH FLEXIBILITY Filed Oct. 30, 1956 t INVENTOR. paw fflmuflrm %MM f (p/W United States TWO-LAYER EXPANSELE LINKAGE OF HIGH FLEXIBILITY David Jacobson, Copenhagen, Denmark, assignor to Rodi & Wienenberger Aktiengesellschaft, Pforzheim, Germany The present invention relates to new improvements in elastic link straps for ornamental or utilitarian purposes, and especially in watch bracelets. More particularly, the invention relates to the type of strap which consists of 'two superimposed layers or rows of links which extend transversely to the longitudinal direction of the strap, and wherein the upper and lower links are staggered relative to each other by the width of one-half link and are resiliently connected with each other so as to be expansiole against the action of springs which are disposed within the links.

The individual links of elastic link straps of this type as previously designed generally consisted of hollow sleevelike casings which were connected with and guided relative to each other by special connecting members. Thus, there has been one prior design of an elastic link strap in which the connecting members consisted of U-shaped connecting brackets, the back portions of which were disposed within the longitudinal side edges of the strap, while the bracket arms extended into the sl'eevelike upper and lower links. When the strap was being expanded or bent, these arms of the U-shaped connecting brackets were turned within the links and thereby tensioned the springs within the links. This prior strap design had the disadvantage of a very undesirable thickness and in the fact that the open ends of the links which formed the outer longitudinal sides of the strap formed very sharp edges which scratched the wearers hand and arm and Wore out his sleeve cufis very quickly. Although it has also been previously proposed to cover up the connecting brackets either partly or entirely along the longitudinal sides of the strap by .means of bent-over tabs on the upper or lower walls of the links, whereby the sharp outer edges of the links were likewise covered, these tabs were again partly unbent when the strap was bent transversely to the direction of its expansion. Such unbending of the tabs considerably affected the ornamental value and appearance of the strap.

Other types of elastic link straps of prior design consisted of only one layer of hollow link casings into which U-shaped connecting brackets were inserted from the longitudinal sides of the strap, which brackets then acted upon leaf springs so as to compress the same in the direc tion of expansion of the strap. In order to prevent the connecting brackets from falling out of the links, two opposite U-shaped brackets were combined into a ring or they were otherwise secured within the links. The disadvantage of these types of straps consisted primarily in the fact that when the strap was expanded, the individual links of such single-layer strap were necessarily separated by gaps which obviously destroyed the desired continuous, unitary appearance of the strap and thus reduced its value.

It is an object of the present invention to provide an elastic link strap or bracelet which overcomes all of the above-mentioned disadvantages of prior strap designs.

More particularly, it is an object of the invention to atent I from tilting over,

ice

provide an elastic link strap which will give a closed unitary appearance even when fully expanded.

This object is attained by making the elastic strap of two superimposed layers of links which extend transversely to the longitudinal direction of the strap, and wherein the links of the upper layer are staggered or off-set relative to those of the lower layer by the width of one-half link.

Another object of the invention is to provide an elastic two-layer link strap, the individual links of which in each layer do not require any special connecting members to connect them to each other.

Another object of the invention is to provide an elastic two-layer link strap which requires no more than three different types of parts for its entire assembly.

A further object of the invention is to provide an elastic two-layer link strap which is considerably thinner than similar straps of previous design.

Another object of the invention is to provide an elastic link strap with smoothly rounded outer edges along the longitudinal sides thereof, and in which there is no danger that the end walls of the individual links will become partly unbent when the strap is being bent transversely to its direction of expansion.

Still another object of the invention is to provide an elastic two-layer link strap which fulfills all the above mentioned requirements and may be manufactured very easily and inexpensively so that the purchase price of such a strap will be relatively low, despite its considerable advantages over similar straps of prior design.

These objects of the invention will all be attained by making both the upper and lower links of the strap in the form of shell-like casings, wherein the upper links are open in the downward direction and the lower links in the upward direction, and wherein the lower links have upwardly extended side walls which project into the upper links through the bottom opening thereof. Each upper link further serves as a housing of at least one pair of curved leaf springs which engage on the one hand against the inside of the side walls, and on the other hand against the inside of one inwardly projecting side wall of each of two adjacent lower links, so that these springs will be pressed flat when the strap is being expanded or bent. For connecting the upper and lower links with each other and to guide them relative to each other during the expanding and contracting movement of the strap and its individual parts, the extended side walls of the lower links are provided, according to the invcrr tion, with inwardly extending slots at the outer ends thereof and at the level of the upper edge of the low end walls of these links. The upper links are then provided with guide portions at the level of the free upper edges thereof. These guide portions of the upper links are inserted into the mentioned slots of the lower links and are guided therein for movement in the longitudinal direction of the strap. They preferably consist of extensions of the end walls of the upper links which are bent over and inwardly toward each other so as to form short tabs which extend transversely to the upper links and in the longitudinal direction of the strap, and which engage in the mentioned slots in the side walls of the lower links and are slidable therein when the strap is being expanded or contracted under the action of the leaf springs in the upper links. These transverse tabs in cooperation with the slots thus serve as connecting means for connecting the upper and lower links to each other and they also serve as retaining means of the loosely inserted leaf springs within the upper links which are preferably notched out at one side of each end so as to form supporting surfaces into which the transverse tabs of the upper links engage so as to prevent the springs particularly at such time during't'he assembly of the strap when the extended portion of the side walls of two adjacent lower links are being inserted into each upper link and between the two springs therein.

Further objects, features, and advantages of the present invention will appear from the following detailed de: scription, particularly when read with reference to the accompanying drawings, in which- Fig. 1 shows an enlarged plan view, partly in cross section, of a portion of the new elastic strap in its con tracted position;

Fig. 2 shows a similar plan view of the same strap, but in the expanded position;

Fig. 3 shows a side view, partly in cross section of Fig. 1; i

Fig. 4 shows a similar side view of Fig. 2;

Fig. 5 shows a cross section taken along of Fig. 4;

line V- V -2,949,'7 29 I I r r A links 12, as indicated in Fig. 8, so that the springs, al-

Fig. 6 shows an enlarged perspective view of a lower v link;

Fig. 7 shows an enlarged perspective view of an upper link in the position as shown in Figs. 1 to 5;

Fig. 8 shows an enlarged perspective view of an upper link, but as seen in an upside-down position to Fig. 7; A

while Fig. 9 shows an enlarged perspective view of one of the leaf springs.

Referring to the drawings, the new elastic strap consists of only three different kinds of elements, namely,

upper links 10, lower links 30, and curved leaf springs 59. 1

Each of the upper links 10 consists of a substantially rectangular hollow casing which is open at the bottom and preferably stamped of a single fiat piece of material so as to form an upper wall 11 which preferably forms the ornamental outer surface of the strap, side walls 12, and end walls 13 which form a part of the longitudinal outer edges of the strap. The outer ends of side walls 12 are provided at the bottom edge thereof with notches 14 of a depth substantially equal to or slightly deeper than the thickness of the material of the casing. End walls 13 are slightly higher than the depth of side walls 12 near their outer ends so that small extensions or tabs 15 are formed which, when the strap is being assembled, are bent inwardly to rest within notches 14 so that the lower surface of these tabs 15 will then lie substantially at the same level as or slightly below the free lower edges of side walls 12.

The lower links 39 are of a shape substantially similar to that of the upper links 10, except as to their end portions. End walls 33 of lower links are of a very shallow height h, considerably lower than the height H of end walls 13 of upper links 10. Furthermore, at the level of the free upper edge of end walls 33, side walls 31 of lower links 30 are provided at their outer ends with slots 32 in which the inwardly bent tabs 15 of upper links 10 are slideably guided. so as to hold the upper and lower links together and to permit them to slide relative to each other in the longitudinal direction of the strap during the expansion or contractionthereof. For this purpose, and so that the upper links 10 will accommodate the lower links 30, the total length L of the lower part of side walls 31 of each lower link 30, that is, below slots 32, is equal to the total length L of each upper link 10, while the upper part of side walls 31 above slots 32 has a length l and is at each end shorter than such total length L by the thickness of end wall 33.

Each upper link 10 contains a pair of curved leaf springs 50, the free ends of which engage against side walls 12, while the curved back portions thereof engage against side walls 31 of two adjacent lower links 30 which, except for the shallow bottom portion underneath the lower edges of slots 32, project into the upper links 10 when the strap is in the assembled condition.

The free ends of springs 50 are notched out at one side so as to form supporting surfaces 51 which may be slipped underneath tabs 15 at the lower side of upper though loosely inserted into links 12, will thus be retained therein and prevented from falling over during the insertion of the side walls 31 of the lower links into the upper links, as subsequently described.

Since the lower 11111630 are staggered or offset in the longitudinal direction of the strap by the width of one-half'link relative to the upper links 10, the portions of one side wall 31 of each of two adjacent lower links above the lower edges of slots 32 are adapted to project, as previously described, into the upper links 10, and one leaf spring 50 is then interposed between each of these side wall portions 31 of two adjacent lower links 30 and the two side walls 12 of one upper link 10. These two springs 50 are flattened out when the strap is either expanded or sharply bent.

When the individual parts of the strap, namely, the upper and lower links 10 and 30 and springs 50, are being assembled to form a complete elastic strap, end walls 13 of the upper links and their tabs 15 which are bent at a right angle thereto are at first still bent outwardly to such an extent as to permit these parts to be fitted together or into each other. Thereafter, end walls 13 will be bent inwardly to the position as shown in the drawings. The respective upper and lower links it) and 30 will then be connected with each other by means of tabs 15 on upper links 10 which engage into slots 3-2 of lower links 30, so that the links of the two layers will then be able to move relative to each other only in the direction of expansion of the strap. In order to permit the strap to bend more easily in a direction transverse to such direction of expansion and also to twist or flex in any direction, it is advisable to make the width and depth of slots 32 slightly larger than the thickness and length of tabs 15 which are guided within these slots.

While the invention has thus been described in detail with reference to certain now preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. Thus, for example, more than one leaf spring may be provided between each side wall 3-1 of the lower links 30 and the adjacent side wall 12 of the respective upper links 10. This may be advisable especially if the strap as a whole should have a relatively large expansion. Such leaf springs are then preferably mounted in the upper links so that the free ends of each pair of springs face toward each other. If, however, only one pair of leaf springs is to be provided in each upper link 10, they may be mounted therein either in the manner as shown in Fig. 1, that is, with their free ends facing toward side walls 12 of upper links 10, or so that both springs face in the same direction.

Having thus described the invention, what is claimed as new is:

1. An elastic link strap comprising: a plurality of upper and lower links each having a substantially rectangular block-shaped configuration the longer dimension of which extends transversely to the longitudinal direction of the strap, said links being superimposed upon each other to form two layers, said upper links being staggered relative to said lower links in said longitudinal direction of the strap by the width of one-half link, each of said links being in the form of a hollow shell-like casing, each of said upper links having an upper wall, opposite side walls, and opposite end walls, and being open in downward direction, each of said lower links having a bottom wall and opposite side walls, and being open in upward direction and having substantially open outer ends, said side walls of each of said lower links projecting at least partly into two adjacent upper links through the lower opening thereof and having slots at the outer ends thereof near said bottom wall, said end walls of said upper links being formed with extensions which are inwardly bent and constitute guide tabs that extend transversely at the level of said slots, said tabs being slidably received within said slots for connecting said upper and lower links with each other and for guiding said upper links for movement relative to said lower links in said longitudinal direction of the strap, the dimensions transversely of the band of each side wall of said lower links being materially less than the corresponding dimensions of the interior of the upper link receiving said side wall, the width and depth of said slots being sufficiently larger than the thickness and length of the tabs they receive to allow the strap to bend and flex transversely about two mutually perpendicular axes transverse to said longitudinal direction of the strap as well as to twist about a third axis extending in said longitudinal direction, and at least one pair of curved leaf springs disposed within each of said upper links and abutting one side wall of each of two adjacent lower links within each respective upper link, each such pair of leaf springs also abutting the two side walls of 6 said respective upper link, whereby said spring will be at least partly flattened when the strap is expanded in said longitudinal direction, or is bent or twisted about the two first-mentioned axes, or is twisted about said third axis.

2. An elastic link strap as defined in claim 1 wherein each outer end of each of said curved lead springs is provided with a cut-out receiving the corresponding inwardly bent tab of the corresponding upper link, said springs thus serving as supports for said tabs and said tabs serving to retain said springs within said upper links.

References Cited in the file of this patent UNITED STATES PATENTS 2,074,046 Ciner Mar. 16, 1937 2,480,015 Goode Aug. 23, 1949 FOREIGN PATENTS 213,632 Great Britain Apr. 1, 1924 

